Membrane applicators are generally unaware of the optimal time-frame for applying a membrane to King Construction Products. Therefore, a study was undertaken to determine the earliest possible date after the placement of King Construction Products that a polyurethane-based membrane can be applied to the surface without the use of a primer. In order to ensure a successful cohesion between the applied membrane and King Construction Product, the concrete must reach an optimum moisture content. However, in order to achieve perfect cohesion between the concrete and membrane layer, the products must first be tested for compatibility. The King Construction Products tested for membrane cohesion can be seen in Table 1, with an accompanying description of each product.
For each product, several mixes were prepared and placed in rectangular plastic containers. The concrete and mortar specimens were allowed to cure and dry at different rates, according to the appropriate curing time for each product. After each specimen was placed, a thin layer of Tremco’s Vulkem 350 liquid polyurethane sealer was applied to the surface of each specimen without the use of a primer. Immediately after applying the polyurethane sealer, a cotton tissue was carefully placed onto the applied membrane.
After 24 hours of curing the cotton tissue was pulled manually to evaluate the cohesion of the membrane. Failure occurred when water saturation was visible in the cotton tissue. The contributing factor to failure was placing the membrane before the concrete was provided with sufficient curing time. A successful membrane application occurred when no visible water saturation was present in the cotton tissue, and the cotton tissue was very difficult to remove from the surface of the membrane. It was found that in order to ensure a successful membrane application to King Construction Products, the concrete must be allowed sufficient moist curing time and dry curing time.
The moist curing period refers to curing immediately after the product has reached initial set, and should be conducted in accordance with ACI 308 “Guide to Curing Concrete”. The drying period refers to allowing the product to remain in a relatively dry condition immediately after the moist curing period. The recommended moist curing time and dry curing time for each King Construction Product before applying a polyurethane-based membrane without the use of a primer can be seen in Table 2.
After performing this study, it is apparent that King Construction Products require the recommended curing and drying times before applying a membrane to the surface. Following these directions will help ensure a successful concrete repair and membrane application when using King Construction Products.
For more information regarding rapid membrane application to King Construction Products, refer to the King Technical Report titled “Rapid Membrane Application to King Construction Products”.